Kavli Affiliate: Blake Sherwin
| Summary:
Ultralight axions (ULAs) are well-motivated dark matter particle candidates that arise in many extensions of the Standard Model of particle physics. ULAs with mass $m_mathrma lesssim 10^-27$ eV have been strongly constrained by cosmic microwave background (CMB) observations in temperature and polarization. We fit recent measurements of gravitational lensing of the CMB from textitPlanck, the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT-3G) using a state-of-the-art simulation-calibrated nonlinear clustering model for ULAs. We derive the strongest constraints on ULAs in the mass range $10^-26;mathrmeVleq m_mathrmaleq 10^-24.5;mathrmeV$. ULAs of this mass have been shown to alleviate tensions between inferences of the matter clustering if they compose a few percent of the total dark matter content of the Universe. We conclude that ULAs with a mass of $10^-26$ eV make up less than 1.5% of the dark matter and $10^-25$ eV axions make less than 9% (both at 95% confidence level). We identify a slight preference for non-zero axion density at $10^-24.5$ eV at $2.1σ$. We find that the preference for ULAs is largely driven by a few data points and that further investigation of non-linear ULA physics is needed to confirm or rule out this signal.
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